second lecture...whee
going to skim ch5 to review BJTs
basic review of bjt operation

small signal general purpose bipolar junction transistors
jfets after, then mosfets
cmos after that

two types, npn and pnp
emitter, base, collector
collector doping is typically ~ 10^6
base doping is slightly higher ~ 10^7 or 10^8
emitter is much higher ~ 10^15
npn arrow is NOT POINTING IN
Ie = Ic + Ib, ALWAYS
the emitter emits electrons for PNP (current in), holes for NPN (current out)
DC beta and DC alpha
beta = common emitter current gain
alpha = common base current gain
beta = Ic/Ib
alpha = Ic/Ie
alpha = beta/(beta+1)
beta = alpha/(1-alpha)
base region/emitter region looks like a diode, but collector is less doped
once the PN base/emitter junction breaks down, the base looks closer to n-type and there isn't enough of a PN barrier remaining to prevent electrons from slipping into the collector region toward the large positive voltage supply
bishop's first law: never trust a manufacturer's datasheet, good as guide, first cut approx, experimentation, there WILL be variation
regions of operation for a BJT
mode		E/B junction	C/B junction	use
active		FB		RB		amp
saturated	FB		FB		switch
cutoff		RB		RB		switch
reverse active	RB		FB		ampish

Ib = 50microamps
Ic = 1milliamp
find:
Ie = 1.05milliamps
beta = 20
alpha = 20/21

early voltage aka early effect - all base current lines converge to a negative voltage on a Vce vs Ic plot

BJT transconductance curve
collector current vs base/emitter voltage, tells us that the voltage won't go much past .7 volts on a PN junction